feat: add phosphor-cron-jobs skill and validate job session_mode at load

[tmaiaroto]

Jobs created by the agent can carry invalid frontmatter — e.g. session_mode: new, which is not one of persistent/ephemeral/per_run. Such jobs were scheduled but skipped at every fire with an unhelpful unknown session mode log line, and the agent had no on-demand reference for writing job files correctly.

• New builtin skill phosphor-cron-jobs (pkg/skills/builtin/) triggers on scheduling/cron/job.md tasks and carries the frontmatter schema, valid session modes, service config, and unattended-prompt guidance. Users can still disable it via disabled_skills or override it with a same-named user skill.
• loadJobFile now rejects unknown session_mode values at load with the valid values named, so misconfigured jobs surface at startup instead of once per fire.
• TestDiscoverBuiltin asserts the new skill's discovery; TestLoadJobFile_RejectsUnknownSessionMode pins the validation.
• Corrected the builtin-skills dev guide, which pointed at the removed internal/skills path.

ஃ Generated with Phosphor

Summary by CodeRabbit

• Documentation
  • Added a guide to configuring and troubleshooting scheduled Phosphor jobs, including session modes, scheduling behavior, and failure handling.
  • Updated the builtin skills reference with the scheduled-jobs guide.
• Bug Fixes
  • Invalid session modes are now rejected when a job is loaded, with an error listing the accepted modes, rather than failing later during execution.

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📝 Walkthrough

Walkthrough

The change adds a builtin skill guide for scheduled Phosphor jobs, updates builtin-skill documentation and discovery tests, and validates session_mode values while loading job files. Unsupported modes now return an error listing the accepted values.

Changes

Scheduled Phosphor Jobs

Layer / File(s)	Summary
Session mode validation internal/platform/cron/service.go, internal/platform/cron/service_test.go	loadJobFile now rejects session modes other than persistent, ephemeral, and per_run. The test checks that the error identifies the invalid field and lists the accepted modes.
Builtin skill guide and catalog pkg/skills/builtin/phosphor-cron-jobs/SKILL.md, .agents/skills/builtin-skills/SKILL.md, pkg/skills/skills_test.go	Adds a guide for scheduled jobs, updates builtin-skill paths and test instructions, and adds discovery assertions for the new builtin skill.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Merge Risk: ⚪ Minimal · up to 2f42f

Unsupported modes now fail during scheduled-job loading. No material regression introduced by this PR is established; the manual UI path’s validation scope remains undefined in the available guidance. Ready to merge after normal checks.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 3 files. (2 skipped: 2 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely identifies both main changes: adding the phosphor-cron-jobs skill and validating job session_mode during loading.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 3 files. (2 skipped: 2 unsupported.)

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Actionable comments posted: 1

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Inline comments:
Review comments at @.agents/skills/builtin-skills/SKILL.md:
- Around line 17-18: Update the embedded-tree reference in the documentation to
point to embed.go in the relocated pkg/skills package instead of the old
internal package location.

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📥 Commits

Reviewing files that changed from the base of the PR and between f7838a5 and 2f42f99.

📒 Files selected for processing (5)

• .agents/skills/builtin-skills/SKILL.md
• internal/platform/cron/service.go
• internal/platform/cron/service_test.go
• pkg/skills/builtin/phosphor-cron-jobs/SKILL.md
• pkg/skills/skills_test.go

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